--- title: "Ultrasonic pulse velocity and tomography tests" subject: "Design of Timber and Masonry Structures" chapter: 8 key: "semester_5/design_of_timber_and_masonry_structures:non-destructive-tests-upv-tomography" source: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/non-destructive-tests-upv-tomography site: BCT Engineering --- # Ultrasonic pulse velocity and tomography tests Design of Timber and Masonry Structures · Chapter 8: Testing of Masonry Elements - Asked in: year not given, 5 marks - Video: [Ultrasonic Pulse Velocity/Echo Testing I Pundit PL-200/PE](https://www.youtube.com/watch?v=BALvC5azIFw) — Screening Eagle Technologies - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/non-destructive-tests-upv-tomography - Whole chapter: https://www.bctengineer.com/md/semester_5/design_of_timber_and_masonry_structures/chapter-8 ## Question Explain the ultrasonic pulse velocity test and elastic wave tomography for masonry. State their uses and limitations. ## Short answer UPV test sends ultrasonic pulses and measures travel time to derive velocity, used to detect voids and estimate dynamic modulus; limited by moisture and heterogeneity. Tomography uses multiple paths to create a velocity map, revealing internal defects and grout success; needs many readings and inversion software. ## Answer #### Ultrasonic pulse velocity (UPV) test A transmitter transducer generates an ultrasonic pulse (typically 50–150 kHz) at one point on the wall, and a receiver picks it up at another. The electronic unit measures the travel time $t$. The pulse velocity is $$ V = \frac{L}{t} $$ where $L$ is the path length between transducers. **Arrangement**: direct (transducers on opposite faces), semi-direct (on adjacent faces), or indirect (same face). Direct is the most reliable. A couplant (grease or gel) is used for good contact. ```text Transmitter )))))))) path L )))))))) Receiver [T]=========== wall ===========[R] \_______ time t _______/ ``` **Uses** - Compare quality: high velocity means dense, sound masonry; low velocity means voids, cracks, loose fill or damage. - Estimate the dynamic elastic modulus: $E_d = \rho V^2\dfrac{(1+\nu)(1-2\nu)}{(1-\nu)}$. - Locate flaws and check grout injection; estimate strength using calibrated correlations. **Limitations**: results depend on moisture, mortar and unit properties, so the correlation to strength is poor; the pulse is scattered in heterogeneous masonry such as rubble stone, and the method needs access to both faces. #### Elastic wave tomography Many source and receiver points are placed around the wall section (or in a grid on both faces). The travel time of each ray is measured by hammer impact or ultrasonic transducers. A computer inversion (e.g. iterative ray tracing) divides the section into cells and finds the velocity in each cell so that the calculated travel times match the measured times. The result is a **velocity map (image)** showing the internal condition. ```text S1 S2 S3 S4 Source points on one side \\\ ||| /// \\ .-------------. cell grid | 2.1 1.4 2.0| velocity (km/s) in cells; | 2.2 [0.8]2.1| low value [0.8] = void '-------------' R1 R2 R3 R4 Receivers ``` **Uses**: finding voids, cracks, delaminations, and the inner core quality of thick stone and multi-leaf walls, and checking the success of grouting. **Limitations**: needs many readings and processing software; resolution is limited by wave length and number of rays; interpretation requires experience. Both tests are non-destructive (no damage to the heritage fabric) and are used together with semi-destructive tests such as the flat-jack test for calibration. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the ultrasonic pulse velocity test on a masonry wall, how is the pulse velocity obtained? A. V = t / L, the travel time divided by the path length B. V = L / t, the path length between transducers divided by the measured travel time C. V = L x t, the product of path length and travel time D. V = frequency / path length Answer: B. The electronic unit measures the travel time t of the pulse between transmitter and receiver, and the velocity is the path length L divided by t. (Key point: UPV principle and formula) 2. A UPV survey on a wall gives a much lower velocity at one location than elsewhere. What is the most likely interpretation? A. The masonry there is denser and sounder B. The transducers were placed on the same face C. Voids, cracks, loose fill or damage are present there D. The mortar there has a higher dynamic elastic modulus Answer: C. High velocity means dense, sound masonry; low velocity indicates voids, cracks, loose fill or damage that slow or lengthen the pulse path. (Key point: Meaning of velocity values) 3. Why is UPV considered a poor direct predictor of masonry strength and unsuitable for some walls? A. It always damages the wall surface B. Velocity depends on moisture, mortar and unit properties, the pulse scatters in heterogeneous masonry like rubble stone, and both faces need access for direct testing C. It cannot be used with a couplant D. It works only on walls thinner than 50 mm Answer: B. Moisture and material variations make the strength correlation poor, scattering occurs in rubble masonry, and the most reliable direct arrangement needs access to both faces. (Key point: Limitations of UPV) 4. How does elastic wave tomography produce a velocity map of a wall section? A. A single transducer pair measures one travel time that is averaged over the wall B. Many ray travel times are measured and a computer inversion divides the section into cells and finds cell velocities that match the measured times C. The wall is cut and each cell is weighed D. A flat-jack is loaded and the deformation is plotted Answer: B. Travel times from many source-receiver paths are inverted (e.g. iterative ray tracing) to get the velocity in each cell, giving an image of internal condition. (Key point: How tomography produces an image) ## Related in Design of Timber and Masonry Structures - [Comparison of masonry units](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Amasonry-units-comparison) — Design of Timber and Masonry Structures, chapter 4 - [Compressive strength test and classification of bricks](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Abrick-compressive-strength-test-classification) — Design of Timber and Masonry Structures, chapter 8 - [Diagonal shear test and flat-jack test calculations](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Adiagonal-shear-flat-jack-numerical) — Design of Timber and Masonry Structures, chapter 8 ## Related in other subjects - [Elastic wave tomography and push shear tests](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aelastic-wave-tomography-push-shear) — Concrete Technology and Masonry Structure, chapter 10 - [Ultrasonic pulse velocity test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aupv-test-interpretation) — Concrete Technology and Masonry Structure, chapter 5, asked 2× - [NDT circumstances; ultrasonic pulse velocity test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Andt-circumstances-upv) — Concrete Technology and Masonry Structure, chapter 5 - [UPV and rebound hammer tests](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aupv-and-rebound-hammer) — Concrete Technology and Masonry Structure, chapter 5, asked 2×